1. Field of the Invention
The present invention relates to recording heads for use with magnetic storage media. More specifically, the invention is a recording head applying a magnetic field at a 90-degree angle to the orientation of the magnetizations within the magnetic storage medium.
2. Description of the Related Art
Recording heads for use with a magnetic storage medium have typically been of the longitudinal type, utilizing a pair of opposing write poles with their tips in close proximity to each other at the bottom surface of the recording head. The two poles are connected typically at the top by a yoke, typically made of a ferromagnetic material similar to that used for the poles. A coil is located in close proximity to one of the two opposing poles. When current passes through the coil, magnetic flux is induced in the yoke which produces a magnetic field with a bubble-like contour, across a gap separating the two poles. A portion of the magnetic flux across the write gap will pass through the magnetic storage medium, thereby causing a change in the magnetic state within the magnetic storage medium where the head field is higher than the medium coercive force. The medium coercive force is chosen high enough so that only the head fields across a narrow gap of a thin film inductive head, flowing with a slider on a air bearing between the surfaces of the disk and the slider, modify the bits of information on the storage medium.
The bits of information are recorded on the disk along concentric tracks that are separated by guard bands. The width of the track plus that of the guard-band in which no information is stored defines the track density. The length of the bit along the track defines the linear density. The total storage capacity is directly proportional to the product of track density and linear density. The increase in linear density also enhances the data transfer rate. The demand for higher storage capacity and higher data rates led to the redesign of various components of disk drives.
The recording densities possible with longitudinal recording are limited to approximately 50 to 100 G bit/inch2, because at higher recording densities, superparamagnetic effects result in magnetic instabilities within the magnetic storage medium.
Perpendicular recording has been proposed to overcome the recording density limitations of longitudinal recording. Perpendicular recording heads for use with magnetic storage medium typically include a pair of magnetically coupled poles, consisting of a main write pole having a small bottom surface area, and a flux return pole having a large bottom surface area. A coil is located adjacent to the main write pole, for inducing a magnetic field between that pole and a soft underlayer. The soft underlayer is located below the recording layer of the magnetic storage medium and enhances the amplitude of the field produced by the main pole. This in turn allows the use of medium with higher coercive force, consequently, more stable bits can be stored in the medium. In the recording process, an electrical current in the coil energizes the main pole, which produces a magnetic field. The image of this field is produced in the soft underlayer, such that about double the field strength is produced in the magnetic medium. The flux density that diverges from the tip into the soft underlayer returns to the main pole through the return flux pole. The return pole is located sufficiently far apart from the main pole, such that the soft material of the return pole does not affect the magnetic flux of the main pole, which is directed vertically into the hard layer and soft underlayer. Strong magnetic recording fields permit the use of high anisotropy magnetic recording medium. Therefore, significantly higher recording densities may be used before magnetic instabilities become an issue.
Regardless of whether longitudinal or perpendicular recording is used, conventional magnetic recording applies the magnetic write fields antiparallel to the direction of magnetization within a domain of the storage medium in order to write a bit. When writing to the storage medium at high speed, there is less time for thermal fluctuations to assist in switching. Therefore, increasing the speed of a write operation requires overcoming a higher thermal barrier. Overcoming the resulting media coercivity requires write poles having increasingly high saturation magnetic fields. Additionally, presently available write poles are fabricated by depositing multiple layers of material from the front of the recording head, working towards the back. Such designs utilize materials having different magnetic properties for different portions of the write apparatus (first pole, connecting yoke, and second pole), and different dimensions for each structure. The width of these structures is controlled by the spinning of photoresist across the surface upon which these structures are deposited, thereby limiting the extent to which the width can be narrowed based on the accuracy with which the photoresist can be deposited. The resulting structure is one which tends to become saturated by magnetic fields at the pole tips.
Accordingly, there is a need for a recording head capable of applying magnetic fields to the storage medium in a manner to better overcome the coercivity of the storage medium material. Additionally, there is a need for a recording head having a write apparatus that is easier to manufacture, for use with narrow trackwidths and high linear densities.
The present invention is a recording head for use with magnetic storage media, wherein the opposing poles of the recording head apply a magnetic field across the trackwidth of the magnetic storage medium, at a 90-degree angle to both the initial and final orientation of the individual magnetizations within the storage medium. The recording head may be used for either perpendicular or longitudinal recording.
The recording head includes a pair of opposing write poles, magnetically coupled by a yoke across their top portions. The distance between the two pole tips corresponds to the trackwidth. The two opposing write poles and connecting yoke may be formed from a single layer of material, having a thickness selected to accommodate the speed at which the magnetic storage medium passes the recording head and the desired linear density.
A coil passes between the opposing write poles. This coil may be any conventional coil dimensioned and configured to induce a magnetic field held within the write poles, connecting yoke, and write gap. Examples include a simple copper or gold coil, a waveguide microstrip, or an asymmetric co-planar strip (CPS).
A second coil is located adjacent to the write poles, and is dimensioned and configured to induce a magnetic field within the storage medium. This second coil may be any coil that is conventionally used, for example, a standard copper or gold coil, a waveguide microstrip, or asymmetric CPS.
A typical magnetic storage medium, such as the disk for a computer hard drive, includes a recording layer having a plurality of magnetically permeable tracks separated by guard bands. As is well known in the art, other layers may be present, for example, the soft underlayer typically used for perpendicular recording, and/or a substrate layer.
To use the recording head, the recording head (or slider) is separated from the magnetic storage medium by a distance known as the flying height. The magnetic storage medium is moved past the recording head so that the recording head follows the tracks of the magnetic storage medium. Current is passed through the coil corresponding to the opposing poles, thereby creating a magnetic flux within these poles. The resulting magnetic field is applied parallel to the trackwidth, corresponding to the hard axis of the track. Each track of the magnetic storage medium will have a hard axis parallel to the trackwidth, and an easy axis parallel to the desired orientation of the magnetizations within each domain. For example, the easy axis for a storage medium used for a longitudinal recording will be parallel to the track (down the track). The easy axis for a perpendicular recording will be perpendicular to both the trackwidth and the path of the track. The magnetic field applied along the hard axis causes the magnetization within the domain currently being acted upon to rotate from its present orientation to an orientation parallel with the trackwidth, along the hard axis. Upon removal of this magnetic field from the domain in question, this magnetization will rotate back so that it is oriented along the easy axis, either parallel or antiparallel to its original orientation. The second coil applies a magnetic field to the domain to ensure that, as it rotates back to the easy axis, it rotates in a desired direction. Current will be passed through this coil in the proper direction so that the appropriate magnetic field is applied for this purpose, according to the well-known right hand rule.
It is therefore an aspect of the present invention to provide a recording head for use with magnetic storage media, applying the magnetic write field perpendicular to the direction of media magnetization, thereby applying maximum magnetic torque to the magnetic domains within the storage medium.
It is another aspect of the present invention to provide a recording head for use with magnetic storage media permitting higher data transfer rates than presently available recording heads.
It is a further aspect of the present invention to provide a recording head for use with magnetic storage media, wherein the opposing write poles of the recording head and their connecting yoke are fabricated from a single deposited or plated layer of material.
It is another aspect of the present invention to provide a recording head for use with magnetic storage media, wherein the opposing write poles may be made quite wide, thereby providing a sufficiently wide path for a strong magnetic field, without adversely affecting trackwidth or recording density.
It is a further aspect of the present invention to provide a recording head for use with magnetic storage media that may be used for either perpendicular or longitudinal recording.
It is another aspect of the present invention to provide a recording head for use with magnetic storage media including means for producing a setting magnetic field for ensuring proper orientation of the magnetizations within the various domains of the magnetic storage media.